I hate to be that guy, but replying to spam is also against the rules guys!
"5. NO Spam: Includes but not limited to: promoting personal sites, making comments which have no discussion value such as "first" or "bump", quote pyramids or empty quoting, battle threads, YouTube spam, "chat" threads, and creating any threads with little to no text where off-site content is linked or embedded. This includes starting forum threads to promote your latest podcast or written review on another site. Additionally, replying to spam & advertising threads is prohibited. Repeatedly bumping and replying to spam will result in your ability to post being temporarily and then permanently revoked."
I am playing on PS3 and have not had any issues summoning or being summoned. Sometimes you get a lot of "summoning failed" messages, but I am assuming that is because someone else grabbed it before you did.
EDIT: Although, I have never been invaded, and my little brother said he tried and it did not work.